text:
Why do the blue angels sometimes dump fuel during maneuvers?
Watching the blue angels I noticed that their was fuel being dumped from the fuel dump nozzle, on top of the vertical stabilizer. Why is this?

That's not actually what you saw. Condensation from pulling G's or otherwise loading the vertical stab - not fuel dumping, which would be pointless, not to mention environmentally unfriendly.

@RalphJ No this wasn't condensation from pulling gs. This was fuel coming from the fuel dump nozzles. The plane was in formation and was the only one doing it. It also was not a smoke trail.

@Boeing787 Do you have photo/video evidence of this? It's highly unlikely: I can only imagine serious pilot error or mechanical failure as explanations. Much more likely is that you misinterpreted what you saw. It can be hard to make out this kind of detail on a jet from a distance traveling hundreds of knots (mph).

https://youtu.be/iMX8NyCdG90
Look at the plane to the left

Either it's smoke trail or the frecce tricolori use green, white and red kerosene:)

The video from the comment yesterday shows the standard smoke generator. "Why only 1 jet was using it then" might be a worthwhile question, but that's the standard smoke.

What about this
https://www.flickr.com/photos/avgeekjoe/20342396120

What you’re seeing there is not fuel dumping, it’s smoke generated from dumping linseed oil into the exhaust of the starboard engine. A Blue Angels F/A-18E/F are specially modified from a stock Rhino, to include, but not limited to, the removal of the 20 mm cannon, and replacement with an oil tank which can feed into the exhaust on command from the pilot.  This produces that characteristic, thick, white, billowy smoke trail for airshows.

Smoke can also be coloured :)

The Blues have done so in the past, but the last time they did was in the early 1970s when the team flew modified F-4J Phantoms with smoke generators installed in dummy Sparrow missile casings on the belly of the A/C.  This was not carried on when the team flew the A-4F and F/A-18A/B/C/D/E/F aircraft.

The video you have linked is way too blurry to give a correct answer (here a link's copy)
On the contrary, the picture you have linked does actually show fuel being dumped (here a link's copy)
Note that video and picture refer to two different episodes, we don't know to which one you are referring to.
On the F-18, fuel dump outlets are on the vertical stabiliser as visible in this cutaway (source):

Fuel is normally jettisoned in case of emergency in order to reduce weight at landing. The picture you've posted might eventually refer to a test.

https://youtu.be/MF_UJ3tQILY look at 43:45 minutes. Fuel is clearly dumped front the top of the vertical stabilizer.

@Boeing787: Interesting to note that it happens just after a cobra manoeuvre. It might be that due to this manoeuvre a bit of fuel escaped towards the outlet and got ejected as soon as the airplane levelled


text:
What are the safety demonstration time-constraints?
On airliners, the safety demonstration includes many items (seat belt, life vest, evacuation, etc.) and each of those items may raise questions from the passengers (when to inflating the life vest, how to unlocking the seat belt, ...) and thus need more time to explain why those items are detailed.
Given the following elements:

the safety demonstration should begin while leaving the gate.
an average passenger may not pay attention for more than few minutes
the briefing should be finished before take-off (I hardly see flight attendants moving and manipulating life vest, seat belts and other objects in the middle of the aisle while taking off)
many items may need a better (and longer) explanation

I have several questions:

Are there any regulations about the timing of the safety demonstrations?
Is it up to the airline (automated videos are quite easy to time)?
What if the safety demonstration are not finished when the aircraft is ready to take off (on the runway with all clearances)?

I'm curious - do you see a lot of passengers asking questions about the safety demonstrations? I don't fly nearly as often as I used to, but here in the US, I've never seen a PAX asking about the demonstrations. I've seen some have trouble buckling the belt, but that's usually dealt with by the crew on their checks through the cabin, not a frantically waved hand or the call button.

@FreeMan Agreed, but not on this website. Perhaps the way safety demonstration is done do not invite PAX to think about it.

On top of Samis answer above, I'd like to add that there are also different requirements for the content (at least in europe):

The life-vest demo is only required if extended portions of the flight are over water and/or climb and approach routes lead over water.
The safety demo has to be finished before take-off.

I remember quite a number of flights where we had to wait at the holding point because the cabin was not yet ready.

I haven't heard of any regulations about the length of the safety demo, just the content, which is pretty much as you described. However it's in the airline's interest to keep it as short as possible. The aircraft cannot take-off before the chief of cabin notifies the cockpit that the cabin is ready for take-off. The cabin is ready after all passengers are on their seats, safety demo completed, galleys secured and hand luggage stowed away.

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sort: votes


text:
Is the heading used near the pole?
If I understand correctly, heading is usually measure relative to the pole (either magnetic or true). Traveling at a constant heading can't be approximated as travelling straight ahead when near the pole. The extreme case being heading to 180° and crossing the south pole.
Althought there are not many aircraft in this situation as explained in this question, using the heading may not be relevant.
How is the navigation handled is such area? Is the heading used?

Near the poles 'polar grid navigation' is used. By placing a rectangular grid over the pole, aligned with the prime meridian, a local coordinate system is created. Aircraft fly constant grid courses near the poles.
For your example crossing the south pole approaching over the prime meridian the true course will change from 180° (T) to 000° (T), but the grid course will remain 180° (G) all the time.
Grid courses and true courses can be converted easily, this youtube video explains it nicely (although he gets the grid track in the wrong direction in the end, it should be 110°(G) instead of 290°(G))

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text:
Are type-C doors plug doors?
As I understand from the answer to this questions, plug doors are larger than the hole they mus fit in so that they are plugged thanks to air pressure, leading to several advantages. Then, I found this video of a type-C door operating. This door does not seems larger then the hole it must fit in and that confuses me.

Is this a plug-door?
Is there something I miss?
Is there other types of door that are not plug-door, or that are plug-door but don't look like plug-door?

No, they are not. Most (not sure if all) Airbus door are not plug-type. And neither are cargo door on most Boeing types.


text:
What is that black pod on the left wing of a TBM?
What is the black pod on the left wing of a TBM?
(Source)

Weather radar. Wish I could afford that kind of stuff. The guy probably has a milkshake dispenser in there, too.

That is the front of the housing which encloses the 10" GWX70 Color Weather Radar antenna.
Here are some close up shots of a TBM depicting the weather radome.

Source: Own work
Note the lightning diverter strips:

Source: Own work
Apart from the simple fact that airborne weather radar is useful, weather radar is a common option due to the equipment requirements imposed on air carriers operating such aircraft. Specifically, in 14 CFR 135.175, the FAA generally prohibits operation without airborne weather radar equipment along routes where thunderstorm activity is forecast.
Many such single engine aircraft include the option for wing-mounted weather radar, as seen on the TBM 900 in the original question. Since weather radar requires a relatively unimpeded area for signal transmission and receipt, the antenna assembly is typically located at the nose of the aircraft, such as on most multi-engine aircraft. In aircraft with nose mounted engines, a mid or outboard wing mounted position makes sense. See the following photos depicting examples of wing mounted weather radar on a Piper PA-46-500TP Malibu Meridian and a Cessna 208B Super Cargomaster, and a nose mounted weather radar on a Beechcraft King Air B200, respectively:

Source: Own work

Source: Own work

Source: Own work
According to the TBM 900 POH, installation of the optional radar system results in a 5 KIAS decrease in maximum cruise performance and a 3 KIAS decrease in long range cruise performance. This change is due to the slight increase in drag from the radar antenna housing.

It is weather radar.
Most multi-engine aircraft have radar in the nose but single engine aircraft mount it on the wing. They have been doing it since WW II, but with night fighter radar.
US Night Fighter Radar

As stated above, it's a dielectric blister fairing which houses the antenna for the GWX70 weather radar.  The single engine requirement for the engine driveshaft and propeller to be mounted on the aircraft centerline as well as interference from the propeller arc required the radar antenna be offset mounted on the wings like this.  Wind tunnel studies showed this configuration minimized parasite drag.  This is a fairly common WX radar antenna installation for single engine aircraft and similar designs are found on the starboard wingtip of the Pilates PC-12 and the antenna pod on the Piper PA-46 Malibu series.

Source: Pilatus Aircraft Ltd.

Source: Piper Aircraft Corporation


text:
Are the number of unique passengers per airport counted?
In airport passenger number statistics, all enplanes and deplanes are added to all direct transfers during a year.
So if I travelled 21 times via Heathrow I was counted as 42 passenger movements at LHR.
Is there anywhere statistics that show the number of unique human beings that travelled via an airport?

This is probably more a question for Travel.SE, although let's see if somebody here has an answer to it.  But short of an agency like the TSA, it may be doubtful that anybody can resolve the 8 counts you had with Airline 1 with the 4 counts you had with Airline 2, etc.  Unless both airlines share your name with a 3rd party, you're probably getting counted by each airline as a unique customer. And even those counts may be something that airlines regard as sensitive information.

@RalphJ You could do this via statistical sampling. You stop a random sample of passengers throughout the year, record their names and how they're travelling, and extrapolate that to the overall count. Similar methods are used in trains and transit systems where there are no ticket gates.

Short answer is no, mostly they are not counted. Even if they have this data it is very unlikely that they publish it.
Assuming that you are not a transfer/transit passenger; meaning you have arrived to airport by ground transportation for your departure and you have left the airport via ground transportation when you have arrived; you will be counted as 42 times in the statistics (21 departure + 21 arrival). This is standard counting method.
If you arrive to the airport by a plane, you stay inside the plane and you leave the airport with the same plane; then you are a transit passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transit passenger)
If you arrive to the airport by a plane, you leave the plane and you leave the airport with the another plane; then you are a transfer passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transfer passenger in this case)
So passengers of an airport are basically; departure + arrival + transit + transfer
(Note: Exact definitions of transit and transfer might change from airport to airport)
Most of the time, especially in smaller airports, airport management does not record passengers on a unique person basis. They simply don't have the unique identifier for each passenger, such as a passport ID number. So they cannot know if a person is travelling first time or fifth time.
However, there are exceptions of course:

There are (very expensive) software that allows airport management to record, filter, manage each passenger data with extreme detail. Its work logic is that it records a special text message that airplane sends to airport before arrival.
For "international" departing/arriving/transfer passengers, this unique traveler information can be obtained from the system of the passport police since they record ID numbers of passports.
Airlines might have this data separately; however this is not a feasible approach since airlines mostly do not share this info.

It will probably depend on the airport, but for example Amsterdam Schiphol airport publishes these numbers every month (in Dutch).
For example for March, there were in to 5 637 767 passengers, of which 7 453 transito passengers (meaning they left on the same aircraft as they came with).
Of the 5 630 314 non-transito passengers, 3 571 116 where O&D passenger (origin / destination passengers), and 2 059 198 transfer passengers (these are double counted).
So for Amsterdam, we can count 3 571 116 passengers who had their origin or destination in Amsterdam, and 2 059 192 / 2 = 1 029 596 unique transit passenger, making the total 3 571 116 + 1 029 596 = 4 600 712 unique passenges (excluding transito passengers).
Passengers transiting between two flights on separate tickets will still be counted twice (there is no easy way to identify them).
Passengers that travel trough the airport multiple times per month are counted multiple times as well.

If the OP travelled to AMS four times in a month (and then back home again) using KLM twice and BA twice, would he show up in those numbers as 8 counts, 4 counts, 2 counts, or 1? A methodology that produces the latter result seems to be what he's interested in.

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text:
What are the dimensions of an NPT pipe for fuel systems?
I have a question about NPT (National Pipe Thread) tapered connectors that are used in fuel systems of several airplanes. Please take a look at this standard-wall one-side threaded nipple (3/4 pipe size, 2" long).
My questions are:
1) How do I decipher the specified pipe size? This one is 3/4, but 3/4 is not any of the dimensions.
2) Why would the unthreaded side have the diameter 1.050"? I want to connect it to a pipe with a 1.0" diameter (yellow color, on the right) as shown in the picture below but I am concerned about mismatch when I use a threadless compression coupler.

Are you sure NPT fittings are used in your fuel system? The problem with NPT fittings is that they require PTFE tape or paste to create a seal, which can break down or enter parts of the fuel system if not properly applied. Many fuel systems employ AN type fittings .

@RonBeyer, you are absolutely correct about AN type fittings. I have to stick to NTP. Even if I can get to AN, I would still like to know why the unthreaded part of the nipple is 1.05". 1" would make more sense, right?

If your question is about dimensions and measurements making sense, you must be from a metric country. Please accept that the old imperial system makes no sense at all.

This Wikipedia page link should help. See the table Standard sizes. Also, directly above that table, see what it says about NPTF.

@mins, that answers my question. Also, I see the problem with a "pipe" that has 1.0" diameter. Such pipes just don't exist. It is a structural tube. A pipe, such size 3/4 would have OD 1.05". This helped me find a mistake in one diagram. Thank you very much.

@curious_1, thank you. I got to know about NPTF.

@Koyovis, you are correct about that.

@mins, could you please write an answer for part 1) and then provide explanation for part 2) from my comment above? I will then mark your answer as solved.

I would just throw in a generic word of caution: If you're not sure about piping/tubing in your aircraft's fuel system, be sure to get an A&P to sign off on your work before you take to the skies, maybe even have him double check your material before you start working. A fuel leak leading to an in-flight engine shutdown would be stressful. A fuel leak leading to an in-flight fire could be fatal.

Mechanical engineering uses a particular wording, I hope I'll not lose myself in the translation... Feel free to correct.
This fitting, standardized in ASME B1.20.1, has the particularity to have conical nut and screw:

The thread is tapered:

Larger diameter ($\small \rm E_2$) = 1.00178 in
Smaller diameter ($\small \rm E_0$) = 0.96768 in
Effective length $\small \rm L_2$ from $\small \rm E_0$ to $\small \rm E_2$ = 0.5457 in

1) How do I decipher the specified pipe size? This one is 3/4
Difference in diameter over $\small \rm L_2$ = 0.0341 in. As $\small \rm L_2$ = 0.5457 in, this is equivalent to 0.75 in per foot (12 in) or 3/4 in/ft.
This is where the size 3/4 comes from.
2) Why would the unthreaded side have the diameter 1.050 in? I want to connect it to a pipe with a 1.0 in
When fully engaged, the screw thread and the nut thread are fully adjusted. The extremity of the screw is at the reference plane (see figure), and the nominal diameter is $\small \rm E_0$
$\small \rm E_0$ is smaller than $\small \rm E_1$, the diameter at the extremity of the nut, both are smaller than $\small \rm D$, the external diameter of the screw.
For a threaded screw, the "diameter" is often the diameter of the unthreaded rod, this is also the case here $\small \rm D$ = 1.05 in.


text:
What happens in a turbine high-temp combustion?
I'm designing an aircraft, and I notice that in high bypass turbofan engines, the fuel is used at relatively low temperatures. So I'm wondering, what happens if the fuel is burned at high temperatures? Does something happen to the metal?

The biggest limiter of hot section temperatures in aviation gas turbines is moving hot section parts subject high stress loads under high temperatures and do so for very long periods of time.  Even the best nickel cobalt superalloys cannot maintain acceptable yield strengths past about 2000°F.  Some additional solutions have utilized to achieve even higher TIT levels such as novel single crystal casting techniques for the rotor buckets as well as using bleed compressor air to envelop the surface of the buckets to protect them against the high temperature exhaust gases.  Some military engines can operate with TITs as high as 2600-2700°F.  Another proposed option has been to manufacture the buckets, stators and hot section casings out of carbon composites, which hold the promise of increasing TITs as high as 4000°F.  However carbon composite blades are susceptible to oxidation before reaching these temps, making it difficult to realize this.  General Electric Aircraft Engines may be on the cusp of solving thes problems; if they do, a composite gas core would offer a quantum leap in power and efficiency.

If you burn it too high, the metal may melt.  If you have the air too hot, the air molecules will become less dense and burn less, therefore, creating less of an explosion and making less thrust. I hope this helps.

Ok. I'll keep that in mind.

First part, yes. Second part, no. Hotter combustion will lead to higher trust (it also means more tightly compressed air to arrive at that temperature). If your combustion chamber didn't melt and nitrogen wouldn't form all those pesky NOx toxins, we would have much more efficient engines.

The fuel-air mixture in gas turbine engines does not explode; it burns with a continuous flame.

If there were an ignition source after the low-pressure system, is there much left in the turbine that would be affected? Would that even allow increased combustion? Also, do NOx compounds occur in combustion, and is it in such a trace amount that it doesn't really have an effect?


text:
Where is the best center of gravity?
I'm designing a plane, and I have a question. What is the best place for the center of gravity, relative to the center of lift? I've heard that it's best put just behind the center of lift, but I would like a second opinion.

Where did you hear that?

It depends on what kind of stability you want the plane to have, see related questions: How does an aircraft tailplane work? and Do any airplane designs exist that don't involve a flight surface that provides downforce?

I would guess that it really depends on how you want the loading envelope to look like. The CG will change depending on different loading characteristics so you should be designing for a load envelope.

I would want the CG to be on the center of lift in terms of front to back, and left to right. In terms of vertical, would it be better to have the CG near the top of the craft or the bottom? (this is assuming the plane is landed and just sitting there, for orientation purposes).

The center of gravity (cg) should be right above or below the center of lift. Otherwise the airplane will start to pitch and never stabilize.
But you do not select the position of the cg, instead, you adjust the center of lift such that lift will act along the same axis as weight. This is called trimming the aircraft and is done by adjusting the elevator deflection (or the incidence of the stabilizer). Of course, you should select the cg position such that the available elevator deflection range will not only shift the center of lift to the cg, but leave enough margin for manoeuvring.
The next condition is to ensure proper natural stability. Once the tail surface produces more lift per area than the forward surface, the aircraft will be instable, so that any angle of attack deviation from the desired state will quickly increase. Therefore, the cg should be placed slightly ahead of the neutral point of the airplane. The neutral point is the cg location at which angle of attack changes will not cause a change in pitching moment. The neutral point of a single wing is near its quarter chord point (it moves forward from the quarter chord point with decreasing aspect ratio), and the neutral point of the whole aircraft is the mean of the neutral points of all components, adjusted for their lift curve slope.
A good first position for the cg is at the quarter chord point of the wing. This ensures that the tail surface will be only lightly loaded, but it might be that stability at this position is not satisfactory. To increase stability (and reduce pitch agility), move the cg further forward, and vice versa. If you want to optimize the aircraft's lift-to-drag ratio (and minimize trim drag), select the most backward cg position with still acceptable stability.
GA aircraft are normally very stable, and their cg position might even be close to the leading edge of the wing. Details depend on tail size, aspect ratios of all surfaces and the desired agility.

Your first statement is NOT correct. Centre of lift is usually behind CG for a normal flight even when the airplane pitch increases. Airplane is stable because of a tailplane which counteracts the moment created by lift acting at CP around CG.
Trimming does not directly affect CP because it does not change wing parameters. The initial reason is a tailplane moment change, and the wing AoA change is the consequence. Then CP really moves (but not for any aerofoil - it does not for symmetrical one), and sum of moments are changing again.

If it would be like you described, the airplane would not require a tailplane at all. All control would be possible with ailerons (symmetric movement for climbing/descending, asymmetric movement for rolling). But that kind of airplane would be dramatically unstable because it is a typical unstable equilibria: any disturbance will cause further increasing change in the same direction. It can be probably good for a fly-by-wire fighter, but not for a civilian airplane, which should be very stable.

@avtomaton: Please consider that your understanding of the center of pressure might be incorrect. And stop hectoring others with false knowledge.

Actually your answer is the first source where I see CP of the whole aircraft consideration instead of wings and a tailplane. Could you please share some references with that terminology? I refer to conventional training books (ATPL books from Jeppesen, Oxford and Bristol), aircraft aerodynamics books and some internet resources like skybrary, avstop.com, flightlearnings.com. Most of them consider CP and Aerodynamic centre of the aircraft as CP/AC of the wings when we are talking about terminology.

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text:
What fuels can turbofans burn?
I know that Jet-A is the fuel most often used for turbofans, but is there something else that these engines can burn? (ethanol, LPG, methane, butane, 100LL, etc.) Basically, can a turbofan burn anything, or are there limits in terms of temperature, combustibility, and so forth? also, which fuel out of any you can think of would be the most powerful/fuel-efficient?

Related: Why do jet engines use kerosene rather than gasoline?

Possible duplicate of Why do jet engines use kerosene rather than gasoline?

Not a turbofan, but the same principals. The military version of the  Rolls Royce Gnome had a long list of fuels that could be used when "needs must" with an inspection required following flight.  There was an even longer list of basically any liquid that will burn with on octane less than petroleum that could be used in war time with an engine strip following.  I can't find a copy of it but do remember that it included cooking oil of many types, fuel oil and diesel.

I do not see the related question answering this question. Very closely related, to be sure, but that question asks, "Why Jet fuel, rather than gasoline?", whereas this question asks, "What can turbofans burn?"

Regarding turbine engines, not merely turbofans, I know some are approved for various types of aviation gasoline, and I have heard an anecdotal report of a turbine engine having been "unwittingly" operated burning 5606 hydraulic fluid. There are certainly quite a list of types of fuel that can be burned with varying degrees of success and engine and component longevity.

Turbine engines for electrical power stations in remote communities burn natural gas.

Somewhat related topic: https://en.wikipedia.org/wiki/Chrysler_turbine_engines - "This engine runs at up to 44,500 revolutions per minute, according to the owner's manual, and could operate using diesel fuel, unleaded gasoline, kerosene, JP-4 jet fuel, and even vegetable oil [...] Chrysler claimed the turbine could gulp everything from peanut oil to Chanel No. 5."

As explained in Why do jet engines use kerosene rather than gasoline?, turbines can burn almost anything, but the lubricating properties of kerosene make the fuel pump simpler as it is otherwise hard to keep high-pressure pump lubricated.
Temperature limiting is simply a matter of sufficiently lean mixture and cooling air stream along the combustor walls.
And most efficient depends on criteria. For money it is definitely kerosene (Jet-A). Actually, Jet-A is an excellent match overall. It is relatively dense (~0.8 kg/l) while still having good specific energy (~43 MJ/kg; so fuels tanks are not too big), lubricates (good for fuel pumps), has quite high flash point (low risk of fire when handling) and is a large fraction of crude oil (C8–C16 (gasoline is just C6–C8) so it is cheap).

Most efficient is in terms of fuel storage(how much can I put in X space) and combustibility(How would I need to change the mixture to be similar to burning Jet-A?).

@Nicholas, for comparing things, you need to either select one criterion, or give each some weight. However, Jet-A is probably optimal for any combination practically useful in aviation.

Indeed. If you intend to use a fuel that has a flame and hot gas temperature that differs too much from it's design fuel, it would require a redesign of the combustion section as usually only about 20% of the air that goes into the 'core engine' (through the compressor section) is actually used for burning and the rest is used to protect/cool the combustion chamber. This is needed, because unlike piston engines, it is a continuous burn.

Not quite anything; fuels with solid combustion products are generally excluded (solid at normal jet engine operating temperatures, that is), because the solid particles in the exhaust do bad things to the turbine blades.  This is why zip fuel (jet fuel with boron compounds mixed in for added oomph) never really took off (pun intended) - that, and also the fact that both the boron-containing additives and the exhaust produced by a zip-fuel-burning engine proved to be hideously toxic.

Jet-A is most common, however, we regularly used mixtures or pure 100LL in the arctic in Twin Otters and Caravans.  Specifically the Caravan was approved for limited 100LL operation.


text:
Is emergency floor lighting fluorescent?
I just read this question (about emergency lighting) for which nobody highlight the title mention fluorecence. As this lighting's requirements include operability with failure of normal electrical power, having fluorescent strip doubling a ramp of lights make sense. However, the pictures illustrating the answers shows seat-mounted lights.
My question focus on the emergency floor lighting installed on the floor. Do this kind of emergency lighting use fluorecent elements?

MikeFoxtrot's answer to the original question quotes an FAA document mentioning incandescent lighting (not fluorescent). I imagine that nowadays they are LED strips for reliability and long life.

I think the term the OP wanted is "photoluminescent", specifically "phosphorescent". I answered accordingly.

@KeithS I don't know the difference between photoluminescent and phosphorescent. I meant the kind of material absorbing radiation and reemitting it as light.

Related

"photoluminescence" is the term for any material that absorbs light of one wavelength and re-emits a different one. Black-light reactive pigments are an example. "Phosphorescence" is a specific type of photoluminescence where the re-emission of light is delayed significantly, and it's the type of photoluminescence used for any "glow-in-the-dark" material.

See US Law the technical means is immaterial, the level of illumination is what is regulated. 2) What is normally meant by fluorescent lighting is a glass tubular enclosure containing mercury vapor. An electric current in the gas excites the mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the bulb to fluoresce (i.e. glow).

@RedGrittyBrick I agree, but I was refering to the title of curious cat's question (mention fluorescent light, maybe not meaning it).

In which case the answer to the title question is "no", emergency lights aren't "fluorescent". However the question details mention operability in total electrical failure, which is not going to happen with a typical fluorescent tube, so I took the leap and figured the term was incorrect for the technology he actually wanted to know about.

@KeithS I don't think "failure of normal electrical power" is the same as "total electrical failure".

@ManuH you're still not going to get enough power out of a battery backup for a fluorescent tube. They work at voltages typically achieved by transforming mains-level AC power. If the main AC power on a plane fails any fluorescent tube light in the cabin will be extinguished.

Fluorescent (more specifically phosphorescent as the re-emission of absorbed light happens on a longer time scale) plastics are sometimes used for exit indicators as they're better than nothing when every other system fails, however they have some drawbacks that limit their usefulness, and so they're not relied on as a primary source of emergency illumination in aviation:

They're not very bright. Even a battery-backup 5-watt incandescent provides more light, and when passengers are trying to find the exit through a cloud of smoke from an engine fire, bright saves lives.
They lose brightness quickly. Here are samples of zinc sulfide on the left and strontium aluminate on the right of each picture. The first picture is immediately after the light source goes out. The second is after just four minutes of darkness:

They rely on external light sources illuminating them for a minimum time. On night flights (when luminescent exit indicators would be most needed), the cabin lights are often dimmed, reducing the effectiveness of photoluminescent strips. Passenger garments overlapping the strips, such as skirts or waist-tied jackets, will have a similar effect on individual strips.
Most pigments react most strongly to UV light which is undesirable for most other purposes. UV light is invisible to us so it's wasted energy, and it yellows plastics (such as cabin trim) which ages airliner cabins more quickly. Light sources that minimize UV are preferable for any purpose except for "charging" photoluminescent strips.
They can't be turned off. When cabin lights are dimmed for passenger comfort on a night flight (letting people sleep etc), the photoluminescent strips will make the cabin look like a cheap Halloween party for up to ten minutes after.

In short, there are better options, especially now with white LEDs that are more efficient and less of a fire hazard than incandescent lights. A simple lithium button battery in the same assembly as the light could keep a 50-lumen LED array going more than long enough even in a complete electrical failure, and LEDs bright enough for this purpose are becoming ridiculously cheap thanks to advances in LED lighting for homes and businesses.

Isn't the OP asking if the floor lighting is made from fluorescent materials or not rather than the advantages/drawbacks. Still, your answer provides some good information.

I really like to see what this "cheap Halloween party" in mid-flight looks like. Do you have references for the exit indicator you mention?

Here's an example of a photoluminescent exit sign for commercial construction: https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcRVJA6kWRGL6hSYy7gguuvvXcY_DsyrzDVvgI8pzIJDew0_-_q_Xw. Imagine that on every seat or regular intervals along the floor.

Here's another example, this time with floor strips: https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRRygIPL9f6BRA6jPexyGeYL84lHs6z0mJlTFwituwGk0tqa21DIA

@KeithS your picture are quite explicit about the use of such strips. You may consider include them in the answer as such (not use in aviation but elsewhere)

That's odd. The florescent strip on the train retains its brightness for something more like an hour.


text:
How is an aircraft with a stabilator trimmed?
Many supersonic fighters have a stabilator to control pitch. My question arises when I cannot see any trim-tab on the stabilisator (e.g. on the F-16 or on the F-22). Other means to trim an aircraft without trim-tab and without using the stabiliser as a trim must exist. What are those means?

Trim is simply a force that offsets the neutral position of the control surface. On aircraft with mechanical controls it is provided aerodynamically via trim tab, but it can also be provided by springs, hydraulics, or simply by adding the selected offset in the fly-by-wire computer. Since F-16, F-18 and F-22 are all fly-by-wire, the last option is most likely.
In fact, all these fighters are aerodynamically unstable, which requires using “cooked” controls where centred stick commands the computer to maintain straight flight and the computer then adjusts the stabilators accordingly, doing small corrections all the time since the flight path would quickly diverge without that. So there is no trim in the traditional sense at all.

Pitch trim on an aircraft with a stabilator is normally accomplished by moving the entire stabilator and holding it in its new trimmed position either mechanically (using the same mechanism as normal pitch control),  aerodynamically (using an "anti-servo tab"), or some combination of the two.
The concept is similar to stabilizer trim as discussed in the other question, only instead of moving the "fixed" forward part of the horizontal stabilizer the entire control surface is moved.
The Pilot's Handbook of Aeronautical Knowledge has a good illustration of an anti-servo tab:

OK for GA, but I fail to see antiservo tab on the fighters mentioned in the question.

For higher-speed designs such as fighters, trim simply involves moving the entire stabilator. Modern FBW systems handle this as a normal part of interpreting pilot input.

@KeithS I believe it's the same on anything else that's fly-by-wire as well: The computer determines the stabilator angle required (including trim) and moves it for you. There's no need for an aerodynamic trim surface in FBW systems because the pilot isn't directly "fighting" the aerodynamic forces, and eliminating it produces a more efficient tail design (no antiservo tab hanging out in the wind to produce additional drag).

@voretaq7 The benefit of trimming the entire control surface is that you are trimming the neutral position of the entire stick, not just reducing the aerodynamic load on it. This means that you can trim for a specific AoA. Non-FBW aircraft also benefit from this design as well.


text:
Are jets deliberately excluded from the "Complex airplane" definition?
A jet aircraft seems for sure very complex as such. But, referring Wikipedia, a "complex aircraft" (as legally defined) has:

A retractable landing gear
Flaps
and A controllable pitch propeller

And there is no propeller in a jet.
What are the reasons of defining "complex aircraft" so that it does not cover jets? Are these reasons other than historical?

What jurisdiction/CAA is this? (FAA, UK CAA, EASA, etc...?)

Related

Well, the complexity associated with variable pitch propeller is not there in a jet either.

All jets require a type rating. Therefore you don't need the complex endorsement directly (other than needing it likely for your commercial checkride, which requires a complex aircraft). The historical training progression is: simple prop, complex single engine prop (requiring the complex endorsement), high performance (200 hp+, though this one is sometimes not gotten), light multi-engine props, and then finally moving into heavier turboprops and then jets which require type ratings.
Note, my answer is FAA specific, and other agencies might have different rules/interpretations for this issue.

A small point, but you can get a type rating without getting your commercial license, so you don't necessarily need to have your complex endorsement in order to fly a jet.


text:
How much damage could a landing gear malfunction do?
How much damage could a total landing gear malfunction do to an airliner? Could the runway wear a hole through the plane?

Related: http://aviation.stackexchange.com/questions/11452/do-runways-need-to-be-repaired-after-gear-up-landings

That's a cool photo.

For an example see https://en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_16 which was written off.

According to Belly landing:

During a belly landing, there is normally extensive damage to the airplane. Belly landings carry the risk that the aircraft may flip over, disintegrate, or catch fire if it lands too fast or too hard. Extreme precision is needed to ensure that the plane lands as straight and level as possible while maintaining enough airspeed to maintain control. Strong crosswinds, low visibility, damage to the airplane, or unresponsive instruments or controls greatly increase the danger of performing a belly landing. Still, belly landings are one of the most common types of aircraft accidents, and are normally not fatal if executed carefully.

It is possible that the friction from a belly landing could wear a hole through the underside of the fuselage. However, even if this were to happen, airliners carry the passengers and crew in the upper half of the fuselage, so nobody would be likely to notice (from inside the aircraft before emergency evacuation).

Additionally most modern airliners have engines extend lower than fuselage, so most damage is to the engines and nacelles, which are designed to be replaceable easily, and the fuselage is only damaged near the tail.

This is highly unlikely -- there is a sturdy keel beam at the bottom of an aircraft's fuselage, similar to a ship's keel.  This beam serves as the main fore-and-aft member in the aircraft structure (its primary function is to transfer bending loads to the center wing box), and will take the brunt of the damage from a belly landing once the belly skin wears through.
Of course, total belly landings are quite rare compared to partial gear landings, which are much kinder on the airframe itself (usually scraping a wingtip and/or an engine pod bottom cowl).


text:
What is an aviation handler?
I was reading this page about Eurocontrol and flight plans. The author refers several times to a "local handler" who apparently assists in dealing with ATC.
What is a handler, who do they work for and what do they do?

Related: Definition, a role part of the Airport Collaborative Decision Making (A-CDM)

@mins from what I'm understanding the job I'm describing is different from a ground handler. Doesn't sound like this person deals with the aircraft itself but assists in other areas for the crew.

I wonder if this isn't connected, I think the definition refers to companies like Aviapartner or Flightcare that are part of the new collaborative process in Europe, and should interface with CFMU to enter e.g. the target off block time if this is not done by the operator directly.

Link is broken.

Handlers are private companies who provide services (for a fee) to pilots and passengers when they fly in and out of an airport.
Depending on the airport, sometimes handlers are required by the local authorities to be used, and other times there are not even any handlers available (a lot of US airports do not have them, for instance).  Often though, they are optional and there to assist crews that are unfamiliar with the procedures at a new airport or who want their assistance as a convenience.
They typically assist with coordinating things like fuel, lavatory service, flight plans, local permits, passenger transportation, catering, coffee/ice/newspapers, etc.  Many times they pay for everything (in the local currency) and provide one consolidated bill for the client to pay.
Note that handlers can be employed by local FBO's (Fixed Based Operators), or they can be part of a larger international company that provides handling services all over the world.  In either case, they are generally coordinating all of the different parties and services needed in order to operate an aircraft in and out of their airport.

This sounds like solid info. However, how does this connect with the ATC aspect of the original question?

They help with the flight plans, which is about the only link to ATC that I can think of.

authors: Аннита Филипповна


text:
How do airports generate "indirect" income?
How do airports generate "indirect" income i.e. income from things other than aviation operations (landing, FBO services, repairs)?

Perhaps this question should ask how do airports generate non-aviation income, rather than how can they. The latter seems very broad and subjective, which makes it a bad fit for SE sites. For example, an airport could smuggle drugs to raise cash, but that's probably not a helpful answer. :) In all seriousness, though, see [ask] for more information about what makes a good SE question.

Asking for the non-aviation income that airports have seems like it could be off-topic, considering that this is a site about aviation.

@fooot That seems like an overly literal reading. If we exclude completely irrelevant lines of business (e.g. drug smuggling, thank you reirab), the question is asking about aspects of running an airport. Specifically, where airports make money besides the obvious sources (terminal rental and landing fees). It's not particularly different from the questions that ask about the expenses involved with running an airline or how commercial airlines pay for fuel.
Just because a question "could" be off-topic doesn't mean it has to be closed.

@ZachLipton I understand your reasoning there. It's just that this question seems further removed from aviation than the others. It's a tough call and I waited until someone else made the first vote. I just wanted to communicate what made it seem off-topic to me and possibly others.

@ZachLipton Honestly, we probably should have closed it as too broad rather than off-topic. While the drug smuggling part was obviously a joke (though an airport would actually be well-suited for this purpose and baggage handlers at major airports have been busted for this,) the question, as originally stated, was extremely broad. The larger airports are practically cities in their own right. For that matter, SeaTac actually is a city. The number of ways that they could generate revenue is pretty much limitless.

One way to approach this question is to look at the annual budget for an airport. I'm going to assume that you mean a large passenger airport as opposed to one focused on serving general aviation, cargo, etc...
Let's use SFO (San Francisco International) as our example. It's a city-owned airport, so the budget is a public document. Here's the budget for FY2014/15 and FY2015/16.
Page 5 (page 7 in the PDF) breaks down major sources of revenue. We have some that fall into the category of "direct" revenue in your question: landing fees, terminal rentals, etc... under the "aviation" category. Some of the terminal rental fees include space for purposes you might not consider aviation uses, like back offices for airline staff We also have $60-80M in "PFC Revenue." PFC stands for "Passenger Facility Charge"; it's a charge that is added to the ticket price of everyone flying out of that airport.
Finally, there are the non-aviation revenues. The bulk of those come in two categories: parking and concessions. Parking is self-explanatory. Concessions describes all the independent businesses that operate at the airport. Many businesses lease terminal space for retail shops (including duty-free), restaurants and take-out food, lounges, currency exchange, etc... They all pay rent and/or a share of revenue to the airport based on the terms of their lease. SFO also books about $23M/year in revenue off the sale of electricity, as the airport sells electricity to its tenants (airlines, concessions, etc...). I suspect, but am not positive, that these electricity sales are a nice moneymaker for the airport, as it can purchase hydropower from the City at extremely low cost and resell it at market (utility company) rates to its tenants. This is a quirk particular to San Francisco however.
If you scroll through the detailed budget in the PDF, you'll find entries for other revenue categories. Examples include advertising fees (Clear Channel pays the airport to put up ads in the terminals and other areas), revenue for things like ATMs and baggage carts, leases to rental car companies, fees paid by taxicabs and airport buses for the right to access airport property, and even permit fees paid by filmmakers and photographers using the airport. Heck, the airport even charges the regional transit agency $3.2M/year in rent and custodial fees for the airport train station. Browsing through the budget should give you a pretty good idea where a large US airport can make money from non-aviation services.

and investment. E.g. Schiphol as a company has a profitable real estate investment and speculation arm, having part ownership in things like other airports, shopping malls, ports, etc. etc.

@jwenting: Those are other activities of the company that owns the airport. I would not consider them indirect income of the airport itself.

Another approach practiced to carrying degrees in various countries: receive massive government subsidies, either in the form of direct cash payments, or capital improvements the airport doesn't pay for.

@JanHudec economically, the company is the airport... Else where do you stop. Schiphol hosts many companies that rent space in office buildings on its premises too. But technically by some definition they're not "the airport" because they're outside the perimeter fence (same as the long term car park, it too is outside the perimeter fence). Or what about the taxi licenses the airport sells without which a taxi operator isn't allowed to pick up fares at the airport? Is that "the airport" doing it or the company operating "the airport"?

When I took an airport management course in college we were taught that parking fees is the #1 source of airport revenue.  I don't have any actual or current percentage numbers to back that up.

Airports tend to acquire a lot of land in their vicinity.
This can be to mitigate noise or complaints from people living under approach/departure paths, for safety in the event of insufficient elevation, for future expansion/extensions of runways or of parking facilities for cars/planes etc.
Grazing animals don't tend to worry too much about airplanes, so "spare" land is often used for agriculture and horticulture (growing animals and plants)  Low income but low costs too.
Some businesses need to be located near to airports for reasons, like courier/freight operations or rental car pickups.  Long-term carparks can be on remote and less-desirable parts of airport land and still generate a profit.  All this land can be re-designated as needs change in the future.
Airport companies will also own the roads across their land.  This can sometimes lead to odd interpretations and loopholes in road laws.  Locally, police cannot ticket a motorist for speeding on airport land roads, because its not public property.  So there are an inordinate amount of speedbumps and sharp turns. Also, bicycles are excluded from some roads used for pickup/drop off.
A motorist pays to use the parking, a traveller pays a departure tax in their ticket, an advertiser pays for billboard or signage space, and a business pays to lease a concession or shop space in the terminal.  Ultimately the visitor pays in the form of increased prices, $10 for a coffee.
The airport company controls everything on their land.  You cannot get a phone line or fibre installed to your site.  Instead, the telco terminates the service in a handover building at the boundary, and the airport company runs the lead-in the rest of the distance.  This is a license to print money because there is no competition so they can charge whatever the customer will pay.
Inside the terminal there are strict controls over transmitters too - you can't even have a wireless ethernet network of your own.  Instead you have to buy a SSID which is configured on the airport's own wireless infrastructure, and trunked back via a VLAN.  Everything costs money every month.    Admittedly this makes sense from a safety standpoint - high power transmitters may have an effect on operations by interfering with aircraft, or more likely interfering with hand-held radios.  And the supply of wireless from a single infrastructure will eliminate contention while providing a better and fairer service.
The stinger comes in the setup and on-going costs being a literal monopoly environment.


text:
What was the Trim Problem on the Brabazon's First Flight?
In this video, starting at 18:15, the copilot on the Bristol Brabazon's first flight recounts that the aircraft became airborne a little sooner than its pilots expected, and that despite the captain holding the yoke fully forwards, the nose continued to rise. The copilot responded by retarding the throttles and then advancing them again, which cleared up the problem. He does not mention any adjustment to the trim, though he states it was fully forwards prior to his action. He also mentions that an adjustment was made to the elevator to fix the problem for subsequent flights.
I am curious as to what caused this problem, and in particular, why it did not recur when the copilot reapplied power. I realize that the copilot may have omitted some key details, such as the aircraft accelerating before the reapplication of power (this occurred at 200 - 300 feet, and the film of the take-off appears to end before it has reached that altitude.) I am also aware, from other reading, that the Brabazon was intended to have a complex (at least for the time) hydraulic control system that was intended to smooth its response to turbulence, that never really worked properly, but it would seem an unnecessary risk to have it engaged for the first flight.

Possible explanations (purely guess work from what is presented): the plane accelerated and the flaps were retracted / the trim is affected by airspeed.

@kevin I imagine the answer is in something like that, but I would guess that with the low wing, flaps would generate an additional nose-down moment. For that matter, if increasing the speed alone decreased the pitch-up, the airplane would be unstable in pitch, would it not? I suppose if the airplane had some sort of linkage mechanism intended to compensate for the pitch effect of the flaps, and it over-compensated as a result of being set up incorrectly, that might do it... but why enable such a mechanism on the first flight, unless the design gave you no choice?

The one thing I have read about this aircraft years ago, is that it had numerous problems in the flight controls, all of them due to the flight controls cables, whose rigging was unstable. I remember having read that it was a  banana (???) effect to the fuselage.I can’t tell  whether it was distortions in the XY plan on in the XZ plan or something else
Reducing the power would it have modified this banana effect?
I can’t tell.

Banana effect sounds like aeroelasticity. To my knowledge it means that angular sensors are located in a different part of the airframe than where their measurement is applied. How that affected Brabazon control is beyond me.

Yeah excessive fuselage flex, reversing the elevator operation. All got re-set by momentarily removing the nose-up pitch moment from the engines. Or something similar.


text:
What is the difference between Body Pitch Rate and Inertial Pitch Rate?
ARINC 429 specifies two series of attitude rate labels for ADIRS/AHRS/IRS systems:
Body

326 : Body Pitch Rate
327 : Body Roll Rate
330 : Body Yaw Rate

Inertial

336 : Inertial Pitch Rate
337 : Inertial Roll Rate
340 : Inertial Yaw Rate

What are the differences between these two sets of values? I'm assuming the Body labels are in reference to the airframe, but do the Inertial labels use a different reference?

Would inertial rates include acceleration on each axis?

@Sami, it's possible. The only other thought I have is that it could be the 3 axis rotation determined by the accelerometers themselves and not from gyros

I'm not 100% sure about ARINC definitions specifically, but in the general aeronautics usage the inertial frame is the ground (flat Earth) frame. The rotation from this inertial ground frame to the body frame is defined by what is known as Euler angles.
Consequently, the inertial angular rates are Euler rates: the rates at which the Euler angles change.
In the body frame, pitch, for example, is what elevator controls, 'up/down' from the point of view of the pilot. Technically, this is pitch motion but not exactly pitch angle control. Euler pitch, the pitch angle per se, is the angle between the horizontal plane and the aircraft body X axis. This angle has a different rate to the body pitch. In an extreme case, on a knife edge (90° roll, zero pitch), body yaw controls pitch angle, and so body yaw rate will match Euler (inertial) pitch rate, and vice versa (minding the sign).
Remember aerospace Euler rotations are in the yaw-pitch-roll order.
Note you cannot rotate angular rates from one frame to another using the same rotation matrix as you use for linear quantities. You need to use the matrix that keeps momentum:
$$
\begin{bmatrix}
\dot{\phi} \\ \dot{\theta} \\ \dot{\psi}
\end{bmatrix} =
\begin{bmatrix}
1 & sin(\phi)tan(\theta) & cos(\phi)tan(\theta) \\
0 & cos(\phi) & -sin(\phi) \\
0 & sin(\phi) / cos(\theta) & cos(\phi) / cos(\theta)
\end{bmatrix}
\begin{bmatrix}
P \\ Q \\ R
\end{bmatrix}
$$
where $\phi, \theta, \psi$ are Euler roll, pitch, yaw; and P, Q, R are body roll, pitch and yaw rates. The aircraft rate sensors measure the latter, so typically you need conversion this way. But for reverse conversion you need to invert this matrix: transposition is not correct for it!
Note this matrix has singularity at pitch ±90°, and indeed, yaw is undefined at such pitch angles. But there are ways to avoid it, e.g. to integrate the whole matrix at every step, or to use quaternions.


text:
Is the IOSA useful even if not all airliners are IATA members?
Given the two facts:

According to wikipedia, the IATA represent a little more than 80% of available seat kilometers. It makes sense as some airlines are not IATA members.
Under each region over the world, an organisation is dedicated to make sure civilian aviation is safe, following ICAO's standards (EASA in Europe, FAA in US, ...)

As I understand, the IATA has its own certification program (IOSA). It seems to me that it doesn't make sense: it doesn't cover all commercial aviation (some low cost carrier are not part of the IATA and still represent a significant part of the traffic), and its purpose is the same as other civilian organisation (FAA, EASA,...) acting under the ICAO's rules.
I'm quite sure I'm missing something, but is the IOSA useful as it does not cover significant airlines and its purpose seems to be covered by other organisations?

IOSA is basically an audit program under IATA. It is not a regulatory regime and as such is different from the FAA, EASA etc, which have force of law. In fact, IOSA is only one of the various audits offered by IATA, which include:

IATA Operational Safety Audit (IOSA)
IATA Safety Audit for Ground Operations (ISAGO)
IATA Standard Safety Assessment (ISSA)
IATA Fuel Quality Pool (IFQP)
IATA Drinking-Water Quality Pool (IDQP)
IATA De-Icing/Anti-Icing Quality Control Pool (DAQCP)

IOSA deals with the operational management and control systems of an airline. The IOSA standards and recommended practices are derived from the ICAO recommendations. From the IOSA  Standards Manual

Sources for IOSA Standards and Recommended Practices (ISARPs)
The safety and security requirements published in the Annexes to the Convention on International Civil Aviation (ICAO Annexes) are the primary source for specifications contained in the ISARPs. Safety and security requirements in the ICAO Annexes used as the basis for ISARPs are those that
are applicable either directly or indirectly to the air operator.

However, these standards are not regulations (as are those defined by FAA etc.):

ISARPs contained in this manual have been developed solely for use under the IOSA program and contain the operational criteria upon which the audits are based. ISARPs are not regulations. (emphasis original).

The usefulness of the IOSA to airlines if from the fact that it is a standard recognized by most other airlines- instead of going to different auditors to ensure compliance of standards, they can agree on a common standard (also IOSA is required for IATA membership).


text:
Can a GPS system be used to identify fixes on conventional instrument approaches?
Is the use of a certified IFR GPS receiver approved for identifying fixes defined by VOR radials, on a conventional (non RNAV) instrument approach?
For example, in KCDW LOC RWY 22, the intersections DOWDY, FAAIR and KOLLI (IF, FAF, step down fix, respectively) are all identified by VOR cross radials (TEB VOR). Can they be identified solely by reference to the GPS database?
Another example would be KABE LOC RWY 13; IZKIP is a step down fix identified by a cross radial from ETX VOR. However, the chart states:

IZKIP FIX MINIMUMS (DUAL VOR RECEIVERS REQUIRED)

Can a GPS be used to identify IZKIP in this case?
According to AC 90-108:

...operators may use a suitable RNAV system in the following ways... Determine aircraft position relative to or distance from...  a named fix defined by a VOR radial.

Therefore my understanding is that named waypoints/intersections defined by VOR radials on a conventional IAP like in the examples above, can be identified using a GPS, except perhaps when the chart requires dual VOR receivers.

good question -- welcome to av.se!


text:
Which countries provide the parameters for their national height reference model in the AIP?
There is a standard in Annex 15 1.2.2.3 "When a geoid model other than the EGM-96 model is used, a description of the model used, including the parameters required for height transformation between the model and EGM-96, shall be provided in the Aeronautical Information Publication (AIP)". According to this provision, I could not find any Country which published the parameters required for height transformation between the model and EGM-96.
For example: Canada uses the Canadian Geodetic Vertical Datum 1928 (CGVD28) as its vertical reference system. The Canadian Gravimetric Geoid 2000 (CGG2000) is the scientific model of the geoid for North America.
I believe this is important for Aviation users. I want to ask if there is any country which is trying to establish the parameters in the AIP?

For AIP Canada uses the NAD 83 which is deemed equivalent to WGS 84, with a maximum vertical difference of 1 m in the area covered by Canada AIP (less than 1% of geoids maximal undulation). As this difference is below GNSS accuracy or any other civil "instantaneous" positioning system, it shouldn't interfere in navigation. See the geoid undulation comparison for Montréal for several gravitational models.

@mins NAD83 / WGS84 describes the ellipsoid, EGM-96 describes the geoid with respect to the WGS84 ellipsoid. The vertical datum in the AIP is sea level (geoid), which is defined by EGM-96 but also by other geoid models. Hence the choice of geoid model is important. For example if the difference is 1 metre, on a 3 degree glideslope that is a horizontal displacement of 20 meters. This is important for GBAS approaches.

@DeltaLima: Under your supervision: NAD83 and WGS84 ellipsoids are nearly identical, so we can get AMSL (orthometric) altitude differences by looking at the geoid height (undulation) differences. CGVD28 reference surface is not a geoid, but HT2.0 hybrid geoid is an approximation at 5 cm. At Montréal, for HT2.0, N = -30.771 and for EGM96, N = -31.5426. The difference is 77 cm which is still small compared to GBAS accuracy of ~1 m.


text:
Do ICAO specifications have the force of regulation?
ICAO, the International Civil Aviation Organization, has specifications for the conduct of civil aviation throughout the world. Such things as the language to be used between controllers and pilots, aircraft calls signs, and a host of other things are covered. At the time of my retirement in 1999, the ICAO specifications were merely recommendations, they did not have the force of regulation in the U.S. or, to the best of my knowledge, in any country in which I operated. Is that still true? Is there any country that says, essentially, that if ICAO says it should be so, the country treats that as a regulation.

See also: http://aviation.stackexchange.com/q/1874/69

According to About ICAO from their own site:

ICAO works with the Convention’s 191 Signatory States and global industry and aviation organizations to develop international Standards and Recommended Practices (SARPs) which are then used by States when they develop their legally-binding national civil aviation regulations.

So ICAO continues to develop standards and recommendations without the force of regulation.


text:
Can the big "X" sign be used for purposes other than runway closure?
About last Sunday night in the dark I was departing LAX on a redeye.  We pulled away from the terminals (maybe 500m?), made a right. Looking back out the window I saw a BIG lighted X (maybe 20? 30? foot high - really bright!) flashing. I guess it was one of THESE but it had four rather than five per arm and REALLY bright.  (I grabbed a completely hopeless video; I'll try to add it later.)
Now, just the previous day there was that incident at LAX where an airliner hit a supply truck, and toppled over the truck (some people in the truck were hurt even I believe).
Can the sign be used on situations other than runway closure? For example:

almost certainly some drama, such as the mentioned truck-jumbo incident, or
is it actually just a normal control sign that goes on an off?  (Perhaps, to indicate "don't cross here, someone else is crossing" - or whatever.)

My impression was that it was at the "side" of a runway  or taxiway, that is to say, as if crossing it.  (Of course, my impression could be totally wrong.)  Would these Xs be used in that way, or, only at one end of a runway?

Is there any specific portion that is not answered in the linked question? The way I see it, the linked question completely answers it. If that is not the case, perhaps you may wish to edit to clarify.

The big "X" is a "don't land here, this runway is closed" indicator. Taxiways that are closed get orange cones and flashing yellow lights, very much like you see for roadway construction. The difference being, the closed runway needs to be obvious as such miles away, while closed taxiways only neef to be understood as closed from a hundred yards away or so.

I edited the question (hopefully) to put more emphasis on what you're asking. If I'm wrong feel free to edit.

no worries, thanks

There are a couple of different NOTAM's stating runway closures at KLAX, including the below. Bear in mind that runways are closed regularly for maintainence (resurfacing) just like roads. No drama about that.

LAX 05/189 LAX RWY 07R/25L CLSD DLY 0800-1300 1705300800-1706011300
LAX 05/157 LAX RWY 07L/25R W 1300FT CLSD. DECLARED DIST: RWY 07L TORA 9665FT TODA 9665FT ASDA 9255FT LDA 0FT. RWY 25R TORA 10808FT TODA...
LAX 05/156 LAX RWY 07L CLSD TO LDG 1705252200-1708190659

There are also several closed taxiways.

Ah, so they can be used for taxiways also?  Thanks.  I was wondering if one of those related to this incident

No, I've never seen the big X used for anything but a runway closure.